Zeroconf
There’s not a lot of webpages out there on the neat things you can do with Zeroconf. For some reason, this surprises me. I feel like it’s a pretty interesting technology, but it doesn’t seem like anyone’s done much with it, despite the fact it’s been around for quite a while. For example, AaronSw wrote about zeroconf more than two years ago.
For those who may have missed the boat, the primary thing that I mean when I talk about Zerconf is automated service discovery (DNS-SD). This is the kind of thing that allows iTunes to see the other computers locally that are also sharing iTunes music. Apple has put a lot of work into making this stuff simple, to the point that it’s one of their more popular open source releases. (Their mDNSResponder code, that is.) I know that Gnome is putting a lot of effort into making things like this work, but I don’t run Gnome (I’m a minimalist) so I don’t know where that’s really at.
Earlier tonight, I was having some problems announcing services over Rendezvous, which is the only way that iTunes will attempt to talk to a DAAP share – there’s no way to tell iTunes “go to this IP address”. This is probably by design: this way I can’t open up someone’s music share that’s not announcing it locally. Kind of annoying for me, since I’d like to be able to play my music from home at work, which I would be able to do with DAAP otherwise After some trouble, I eventually got my machine to announce the iTunes share (which is done via mt-daap) on my Linux box, so I can now play that music. I also added a few other Services: HTTP and SSH. Still, I don’t really know what I can do with these. Why doesn’t putty or some other app capitalize on this by offering to search local hosts for SSH? Does no one really use local services that this could make easier?
My Zeroconf stuff comes from Howl, which offers a multi-platform open-source solution to providing Zeroconf services. It’s a decent library, with decent tools. It is a bit iffy on the user-level: The error messages are pretty unspecific. For example, if you try to announce a service before first running mDNSResponder, it will give an error message that it is unable to connect: but won’t tell you where or why, nor is it mentioned in any documentation (that I can find). The code itself seems solid, however, and is working well here. So, what cool ideas are there for Rendezvous that no one has done anything with? And who’s going to step up to the plate to start?
One example I can think of: set up Rendezvous to announce your local MySQL servers. Then, if you’re in an office where you do development, you can just pick from a drop down of development servers: you don’t have to depend on static IP addresses, you can just scroll through a list. You can even use the text fields of the Rendezvous to include a Guest login. Seems like something that would work well for CocoaMySQL. Of course, it doesn’t look like it’s been touched for more than a year, so it’s not likely to change in the near future. Just an idea.
What zeroconf does not do, which many people don’t seem to understand, is provide any real help in actually creating the connections. Lots of people, myself included, seem to think “Rendezvous” is this magical tool that does all the network communication for you. (That is, I used to think that way – I know better now.) Really, all it does is give you an IP address – nothing that a relatively tech savvy person couldn’t do on their own, at the application level. The communication actually takes place over the typical channels – regular socket communication.
So, although Zeroconf/Rendezvous is cool, it’s not an “end all/be all” to network communication. Just something to keep in mind.